Echo has a Windows path traversal via backslash in middleware.Static default filesystem

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS

5.3 · CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N

EPSS

• CVE-2026-25766: 0.38% estimated exploitation activity in the next 30 days; percentile 32.35 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

Summary On Windows, Echo’s middleware.Static using the default filesystem allows path traversal via backslashes, enabling unauthenticated remote file read outside the static root. Details In middleware/static.go, the requested path is unescaped and normalized with path.Clean (URL semantics). path.Clean does not treat \ as a path separator, so ..\ sequences remain in the cleaned path. The resulting path is then passed to currentFS.Open(...). When the filesystem is left at the default (nil), Echo uses defaultFS which calls os.Open (echo.go:792). On Windows, os.Open treats \ as a path separator and resolves ..\, allowing traversal outside the static root. Relevant code: - middleware/static.go (path unescape + path.Clean + currentFS.Open) - echo.go defaultFS.Open → os.Open This is the same class as CVE-2020-36565 (fixed in v4 by switching to OS-aware cleaning), but in v5 the path.Clean + defaultFS combination reintroduces the Windows backslash traversal. PoC Windows only. Sample code…

Published by the source

17 Feb 2026, 18:53 UTC

Last modified by the source

27 Feb 2026, 22:07 UTC

Source last checked

26 Oct 2026, 15:14 UTC

1. Revision 1 · created · 26 Oct 2026

   Published from ghsa record GHSA-pgvm-wxw2-hrv9

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# Patch Next advisory brief: CVE-2026-25766

Advisory: Echo has a Windows path traversal via backslash in middleware.Static default filesystem
IDs: CVE-2026-25766, GHSA-pgvm-wxw2-hrv9
Record: https://patchnext.com/advisories/cve-2026-25766 (revision 1, source checked 26 Oct 2026, 15:14 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Medium (CVSS 5.3)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: github.com/labstack/echo/v5 5.0.3. A vendor fix does not mean a deployment is fixed.

## Affected components
- Go github.com/labstack/echo/v5: affected >= 5.0.0, < 5.0.3; fixed in 5.0.3

## Suggested inspection (read-only)
- Go github.com/labstack/echo/v5: check the installed version with your package manager.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on github.com/labstack/echo/v5.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://github.com/advisories/GHSA-pgvm-wxw2-hrv9 (GitHub-reviewed advisory GHSA-pgvm-wxw2-hrv9 lists affected ranges: Go github.com/labstack/echo/v5 >=5.0.0 <5.0.3)

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